20"Obsession + Argo Navis + Servo Cat = GOTO BLISS !!!!

Dave,

I am impressed! In retrospect, has it been worth it?

WOW Dave looking good. I assume you can now track and image with the system?

One critic. Remove the wheelie bars and put it on rubber tracks to make it look like a US unmanned battle tank :lol:

After the WSP this year where someone knocked the scope out of position just before Chris Lintot was going to look through it,

The worst excuse I have ever heard for someone buying new gear!

WOW Dave looking good. I assume you can now track and image with the system?

Up to a point - because the 20" Dob is an Alt-Az mount there will be noticable field rotation on images longer than a few seconds, especially at the celestial equator. You could take lots of short images and then rotate and stack them... which is why this system is especially suited to webcam imaging. There are a few packages out there for doing "drizzle" tracking, where each frame is automatically rotated as you record an AVI movie.

Alternatively you can use a field de-rotator to correct for field rotation during a long exposure. I've built one for my own 20" but haven't used it yet - lots of other probs to overcome first!

Phil.

Lads,
Thanks for the kind words, it should be able to do planetary webcam imaging no problem, it'll be down to how good the seeing is more then anything else for this scope, when its good the planetary views are amazing.
As for DSLR imaging, when I give that a go, I'll be imaging very near the meridian so that there is minimal field rotation, I've heard nothing but hardship and grief on the web with field de-rotators and currently don't plan on getting one.
Phil, how did you go about making it, have you any pics of it?

has it been worth it?

we'll, when I looked at Saturn with 500x with good seeing earlier this year before we lost it behind the sun, the one thing that really annoyed me was that after about 10 seconds you had to nudge the scope and 10 seconds later again and again to the point it was driving me abit mad, I really missed the comfort the LX200 gave interms of just keeping the object in the FOV.

One critic. Remove the wheelie bars and put it on rubber tracks to make it look like a US unmanned battle tank :lol:

that would make it an all terrain scope, great idea!

The worst excuse I have ever heard for someone buying new gear!

That was the straw that broke the camels back for me. :lol:
M51 was practically on the horizon and was barely visible and fading, when it was lost I was unable to get it back. Original excuse don't you think. :lol:

Up to a point - because the 20" Dob is an Alt-Az mount there will be noticable field rotation on images longer than a few seconds, especially at the celestial equator.

interesting, I would have thought that it was the zenith would have the worst rotation as the scope does a full 180 once it crosses the meridian.
I found with experimenting with the ETX70 (when I had it) that the celestial equator was not so bad, it seems to me that the altitude drive was going at its slowest there compared to near the east/west horizon. Less altitude motion means that one drive (azimuth) is most of the motion making the scope as close to an equatorial as it can get.
Do I feel another "oh god, its not another M42 shot " on the way. :lol:

but, as far as this scope goes for me, its main use is viewing, imaging is secondary.

Cuh! You sold out - so much for remaining a "real" astronomer with encyclopaedoic (if erroneous) knowledge of hundreds (ok, dozens!) of deep sky objects!

Phil.
(Disgusted of Bray.)

ya know, goto convenience has a cost, I always kinda feel that equipment can get in the way of looking at the sky, setup is real quick on a manual scope and many of you out there know what a complete chore setting up a goto scope can be like, Originally, I honestly had no intention to GOTO-ising this scope when I got it.

Hope you get a few good nights over Christmas to play with in.

god knows now we'll get storms and hurricanes now that I have it working. :lol:

As for DSLR imaging, when I give that a go, I'll be imaging very near the meridian so that there is minimal field rotation, I've heard nothing but hardship and grief on the web with field de-rotators and currently don't plan on getting one.
Phil, how did you go about making it, have you any pics of it?

Dave - I'll try and take a few photos of the insides of the de-rotator if I get time over Christmas - remind me if I don't! It's not rocket-science to build one, just a little care and attention. I built mine using a small stepper motor from a 5.25" disk drive and a DIY plastic gear using M6 Nylon threaded rod and a few bearings.

Up to a point - because the 20" Dob is an Alt-Az mount there will be noticable field rotation on images longer than a few seconds, especially at the celestial equator.

interesting, I would have thought that it was the zenith would have the worst rotation as the scope does a full 180 once it crosses the meridian.

D'oh! As usual, I engaged fingers before thinking - you're quite correct - zenith=badlands!

Looking at your photos, it looks like you have the same motors as I have for the 20" equatorial I'm building for the observatory - Pitmann servos. I'm using the SiTech controller ( www.siderealtechnology.com/ ) which can either be used driven by an Argo Navis or direct from the PC (as I suspect yours can too) so that you can turn it into a point-and-click-GOTO system using a planetarium program like The Sky, Cartes du Ciel, or similar.

Phil, I have alot of the motor taped up as there was a small exposed circuit board there, fine for Arizona but imagine what dew might do to it here!.
and yes you are bang on the money, it can be run using a planetarium program.
You'll find that these motors are just the job for what you're doing with them.